The present invention relates to an ultraviolet/infrared absorbent low transmittance glass. More particularly, it relates to an ultraviolet/infrared absorbent low transmittance glass which has an almost neutral color such as bluish green shade or deep green shade, low visible light transmittance, low solar energy transmittance, and low ultraviolet transmittance, so that it is useful for windows of vehicles or buildings particularly for a privacy protecting glass of vehicles and more particularly for reducing the thickness and weight of these windows.
Recently, a variety of glasses with ultraviolet/infrared absorptivity to be used as a vehicle windshield have been proposed with the view of preventing degradation of luxurious interior materials and reducing cooling load of the vehicle. In view of privacy protection, glass with relatively low visible light transmittance is preferably used for a rear window glass of a vehicle. Such kinds of glasses include the followings.
For example, a dark gray colored infrared absorbent glass disclosed in Japanese Patent H7-29813B consists of soda-lime-silica glass including colorants consisting of 1.00 to 1.7 weight percent Fe2O3 (total iron), at least 0.27 weight percent FeO, 0.002 to 0.005 weight percent Se, and 0.01 to 0.02 weight percent CoO. The glass exhibits luminous transmittance less than 32 percent and total solar infrared transmittance less than 15 percent at 3.9 mm thickness.
A dark gray colored glass disclosed in Japanese Patent H8-157232A consists of soda-lime-silica glass including colorants consisting of 0.8 to 1.4 weight percent Fe2O3 (total iron), less than 0.21 weight percent FeO, 0.05 to 1.0 weight percent TiO2, 0.02 to 0.05 weight percent CoO, and 0.0005 to 0.015 weight percent Se.
A neutral gray colored glass disclosed in claim 25 of U.S. Pat. No. 5,393,593 includes a base glass consisting of 66 to 75 weight percent SiO2, 10 to 20 weight percent Na2O, 5 to 15 weight percent CaO, 0 to 5 weight percent MgO, 0 to 5 weight percent Al2O3, and 0 to 5 weight percent K2O, and colorants consisting of 1.00 to 2.2 weight percent Fe2O3 (total iron), at least 0.20 weight percent FeO, 0.0005 to 0.005 weight percent Se, and 0.010 to 0.030 weight percent CoO. The glass exhibits luminous transmittance less than 35 percent and total solar infrared transmittance less than 20 percent at 3.9 mm thickness.
The glass of neutral color disclosed in the PCT (Japanese phase) H8-506314 consists of soda-lime-silica glass including ferrous iron calculated as follows:
FeO(weight percent)xe2x89xa70.007+(optical densityxe2x88x920.036)/2.3, also including 0.25 to 1.75 weight percent Fe2O3 and one or more colorants among Se, Co3O4, Nd2O3, NiO, MnO, V2O5, CeO2, TiO2, CuO and SnO. The glass exhibits visible light transmittance not less than 32%, ultraviolet transmittance not greater than 25%, solar energy transmittance which is less than visible light transmittance by at least 7%, and the dominant wavelength preferably less than 570 nm at 4 mm thickness. Some of these examples can be used for a privacy protecting glass.
In both the dark gray colored infrared absorbent glass disclosed in the Japanese Patent H7-29813B and the deep gray colored glass disclosed in the Japanese Patent H8-157232A, great quantity of Se is used for obtaining a desirable color. Se is toxic and easy to vaporize, so that great quantity of Se is unpreferable for the environment and should be avoided.
The neutral dark gray colored glass disclosed in U.S. Pat. No. 5,393,593 is also unpreferable for the environment because great quantity of Se is contained. Great quantity of FeO is preferable for the heat rays absorptivity, but unpreferable because FeO selectively absorbs the infrared light in a range from 1000 to 1200 nm which is the most efficient range in brightness distribution of flames for producing glass with a usual furnace, and reduces the temperature of the molten glass in the bottom of the furnace which causes various defects.
The foregoing glass which exhibits low visible light transmittance is excellent in privacy protection, but the glass has disadvantages in that it is difficult to see the scenery through the glass. On the other hand, the glass exhibiting a middle transmittance satisfies both privacy protection and safety to some extent. At present, these two kinds of glasses are chosen according to the parts of vehicles or situations.
The aforementioned glass includes selenium in high concentration to provide desired optical properties, without essentially including nickel.
The glass available for privacy protection disclosed in PCT(Japanese Phase) H8-506314 exhibits the neutral color shade by including all kinds of colorants of Ni, Se and Co. However, the glass contains great quantity of Se since Ni content thereof is low.
To solve problems of the prior art mentioned above and to provide the ultraviolet/infrared absorbent low transmittance glass which has a desired almost neutral color such as bluish green shade or deep green shade, low or middle visible light transmittance, low ultraviolet transmittance and low solar energy transmittance with extremely smaller quantity of Se than the prior art or without Se, the applicant proposed the ultraviolet/infrared absorbent low transmittance glass (Japanese Patent H10-114540A) consisting of base glass comprising:
65 to 80 wt. % SiO2;
0 to 5 wt. % Al2O3;
0 to 10 wt. % MgO;
5 to 15 wt. % CaO wherein a total amount of MgO and CaO is between 5 and 15 wt. %;
10 to 18 wt. % Na2O;
0 to 5 wt. % K2O wherein a total amount of Na2O and K2O is between 10 and 20 wt. %; and
0 to 5 wt. % B2O3,
and a colorant including:
1.2 to 2.2 wt. % total iron oxide (T-Fe2O3) expressed as Fe2O3;
0.001 to 0.03 wt. % CoO;
0 to 0.0008 wt. % Se; and
0 to 0.2% NiO.
The ultraviolet/infrared absorbent low transmittance glass disclosed in the Japanese Patent H10-114540A exhibits relatively low visible light transmittance, low solar energy transmittance and low ultraviolet transmittance. This ultraviolet/infrared absorbent low transmittance glass exhibits the visible light transmittance (YA) measured by using standard illuminant xe2x80x9cAxe2x80x9d in the range about 23 to 50 percent and the solar energy transmittance (TG) in the range about 20 to 35 percent at 4 mm thickness.
Development of low fuel efficiency system, weight reduction of vehicle""s body and the like have been in progress in recent years in order to reduce the environmental load generated by vehicles. The weight of the vehicle has been reduced by thinning a steel plate of the body while increasing the strength. Now, still more weight reduction of the vehicle""s body has been desired by thinning the window. However, thinning the glass increases the visible light transmittance and solar energy transmittance. An ultraviolet/infrared absorbent low transmittance glass which has sufficiently low visible light transmittance and sufficiently low solar energy transmittance even with a thinner thickness has been desired for reducing thickness and weight of vehicle""s windows, but has not been provided yet.
The ultraviolet/infrared absorbent low transmittance glass disclosed in the Japanese Patent H10-114540A exhibits the visible light transmittance in a range from 10 to 25 percent and solar energy transmittance in a range from 10 to 35 percent at 3.1 to 5 mm thickness.
However, it has been desired to develop a still lower transmittance glass which has low visible light transmittance and still lower solar energy transmittance, for example, the visible light transmittance of 10 to 25 percent and solar energy transmittance of 10 to 35 percent at 2.8 mm thickness, in order to reduce the thickness and weight of vehicle""s windows.
The glass should have the visible light transmittance in a range from 5 to 15 percent and solar energy transmittance in a range from 5 to 25 percent at its thickness of 4 mm in order to have the visible light transmittance in a range from 10 to 25 percent and solar energy transmittance in a range from 10 to 35 percent at 2.8 mm thickness.
It is an object of the present invention to provide an ultraviolet/infrared absorbent low transmittance glass which has almost neutral color such as bluish green shade or deep green shade, low visible light transmittance, low solar energy transmittance and low ultraviolet transmittance so that it is useful for a window of vehicles or buildings particularly for a privacy protecting glass of vehicles more particularly for reducing the thickness and weight of the windows.
The ultraviolet/infrared absorbent low transmittance glass of the present invention consists of a base glass, that is, the major constituents comprising 65 to 80 wt. % SiO2, 0 to 5 wt. % Al2O3, 0 to 10 wt. % MgO, 5 to 15 wt. % CaO wherein a total amount of MgO and CaO is between 5 and 15 wt. %, 10 to 18 wt. % Na2O, 0 to 5 wt. % K2O wherein a total amount of Na2O and K2O is between 10 and 20 wt. %, and 0 to 5 wt. % B2O3, and a colorant including, 1.2 to 2.2 wt. % total iron oxide (T-Fe2O3) expressed as Fe2O3, more than 0.03 wt. % CoO, less than 0.0001 wt. % Se, and 0.08 to 0.2% NiO, and the glass has the visible light transmittance (YA) measured by using standard illuminant xe2x80x9cAxe2x80x9d not more than 12 percent at 4 mm thickness.
The ultraviolet/infrared absorbent low transmittance glass of the present invention realizes a low visible light transmittance (YA) not more than 12 percent at 4 mm thickness by increasing CoO more than that included in Japanese Patent H10-114540A while comprising little or no Se.